Transistors, such as power MOSFETs, are widely used as electronic switches for switching electrical loads, such as motors, lighting, and others, or as switches in switched mode power supplies, to mention only some possible applications. Power MOSFETs include a drift region between a body region and a drain region, where a PN-junction is formed between the body region and the drift region. The MOSFET is switched off when a voltage is applied that biases the PN-junction in a reverse direction, so that a depletion region is formed in the drift region. A doping concentration and a length of the drift region are two of several parameters that define a voltage blocking capability of the MOSFET. The voltage blocking capability is the maximum voltage that may be applied to the PN-junction before an Avalanche breakthrough occurs. When an Avalanche breakthrough sets in a high current flows through the MOSFET in the reverse direction, this current causes the MOSFET to be heated.
Dependent on the specific type of the MOSFET, the voltage blocking capability can be between several 10V and up to several kilovolts (kV). Modern MOSFET device are capable of withstanding an Avalanche breakthrough for a while without being damaged or even destroyed. The robustness of a MOSFET is defined by the energy it may dissipate in the Avalanche breakthrough state without being damaged or destroyed.
There is a need to further improve the robustness of MOSFET devices.